Field
Apparatuses and methods consistent with exemplary embodiments relate to a display apparatus, a light source driving apparatus and a driving method thereof, and more particularly a display apparatus, a light source driving apparatus and a driving method thereof, in which a driving current of a display is controlled.
Description of the Related Art
A display apparatus includes a driving section, i.e., a driver, for controlling a constant current for operating a light source such as a light emitting diode (LED), and the driver performs constant current control and brightness control of the light source.
A driving method of the driver is classified into at least a linear type, a switching type using a boost converter or a buck converter, etc. The linear type includes a bipolar transistor or a metal oxide field effect transistor (MOSFET) and a constant current control circuit. The boost converter or the buck converter used in the switching type has a power stage that includes a control circuit for applying pulse width modulation (PWM) or pulse frequency modulation (PFM) to an input voltage, a switching diode, a capacitor, an inductor, etc.
Although the linear type has been generally used in a mobile device or the like because it has a simple control circuit and does not need an inductor, diode, capacitor, and other elements of the switching type, the linear type disadvantageously has a lower efficiency than the switching type. On the other hand, the switching type has a high efficiency but has a disadvantage that the boost converter needs separate dimming software or the buck converter needs a large secondary winding number and a high voltage.
FIG. 1 is a view showing operations of a linear type driver in the related art.
As shown in FIG. 1, the conventional linear type driver performs the constant current control by operating a base/gate of the transistor in an active region as a voltage controlled current source (VCCS) that acts like a variable resistor in accordance with levels of a base current/gate voltage. Here, loss occurs due to a dropout voltage generated between opposite terminals of the transistor in accordance with an input voltage at the constant current control.
As shown in FIG. 1 a display apparatus using LEDs as a light source may have a structure where a plurality of channels 11 and 12, each having a plurality of LEDs connected in series, are connected in parallel. FIG. 1 shows an example where there are two LED bars 11 and 12 corresponding to channels, each of the channels 11 and 12 including eighteen LEDs, and a current of 0.45 A and a voltage of 64V are applied thereto.
In the linear type, if a predetermined voltage (e.g., 64V) is supplied to the plurality of LED channels 11 and 12, a difference in forward voltage drop (hereinafter, referred to as “VF”) may exist among the LEDs. For example, the VF of a single LED may be between 2.7V to 3.6V.
Specifically, referring to FIG. 1, the VF may differ from the minimum of 49V(VF(MIN)*18EA=49V) 11 to the maximum of 63.5V(VF(MAX)*18EA=63.5V) 12 in accordance with the resistance of the LEDs. Therefore, a low voltage 49V is supplied to a channel 11 to which the LED having the low VF is applied, and thus a relatively high voltage 15V is supplied to the linear circuit, thereby causing a power loss (PLOSS) (e.g., 7.218 W) in the linear driver circuit. Accordingly, a dropout voltage of the transistor included in the linear circuit increases and heat is intensively generated, lowering reliability and efficiency.
The linear type LED driver is in high demand because a control circuit is simple. However, as described above, the conventional linear type has problems of low efficiency and power loss caused by the dropout voltage in the constant current control.
Also, in the case of multi-channels as shown in FIG. 1, the loss of the driving circuit may be unbalanced among the LED channels. The VF of the LEDs varies widely and is difficult to be managed during manufacturing. The difference in loss due to the VF among the LED channels similarly varies widely and is difficult to manage in manufacturing a backlight unit, and, therefore, an additional heat-radiating design is needed.